In general, as a safety device for protecting an occupant, an airbag apparatus is provided in a vehicle, and at the time of an accident, gas generated from an inflator flows into an airbag cushion such that the airbag cushion is inflated to protect the occupant.
The airbag apparatus is installed at each part of the vehicle as necessary, and there are a driver airbag (DAB) which is mounted on a steering wheel to protect a driver, a passenger airbag (PAB) which is mounted at an upper side of a glove box to protect a passenger seated in a front passenger seat, and a curtain airbag (CAB) which is mounted along a roof rail to protect a side of an occupant.
The airbag apparatuses are operated as an airbag control unit (ACU) controls the inflator, which is a gas generating means, in accordance with a signal detected by a sensor that senses a vehicle accident.
That is, when gas is generated as a gas generating medium in the inflator explodes by a control command of the ACU, the gas flows into the airbag cushion, and the airbag cushion is inflated and deployed by pressure of the gas flowing into the airbag cushion, thereby protecting a passenger.
However, in a case in which internal pressure in the airbag cushion is low for the latter half of a period when the airbag cushion is deployed at the time of a high-speed collision of the vehicle, severity of injury to the neck is increased. On the contrary, in a case in which the internal pressure is high, severity of injury to the head is increased.
In a case in which a closed vent is applied to the airbag cushion and the number of vent holes is increased in order to reduce injury to the occupant, impact to the head of the occupant is delayed by the airbag cushion, but severity of injury to the head tends to be increased at a point of time at which a vent hole is closed.
In a case in which an active vent with an open structure is applied to the airbag cushion, the severity of injury to the head of the occupant may be reduced, but there is a problem in that the severity of injury to the neck is increased.
In order to prevent the aforementioned problem, a lower risk deployment (LRD) vent is provided in the airbag cushion, and the LRD vent is closed at a point of time at which the airbag cushion is fully deployed, thereby reducing the severity of injury. However, there is a problem in that the LRD vent increases costs and the number of working processes.